The invention relates to a process for recovering acidic gases collected by gas desulfurization. These acidic gases (which are sulfides) are either thermally dissociated in a Claus furnace or are transformed into sulfuric acid,
Solid and liquid hydrocarbon-containing fuels generally contain sulfur. With gasification of the fuel, hydrogen sulfide, H.sub.2 S, and carbon oxysulfide, COS, are formed. The gasification is generally intended to produce hydrogen, and synthesis gas or reactants used for the oxo process. The presence of the sulfide gases is a considerable impediment to subsequent processes using the intended gases. Consequently, these sulfides must be removed by an appropriate scrubbing process. The thus-isolated sulfur-containing compounds are environmental hazards, so they cannot be discharged into the atmosphere after being separated from the scrubbing solution. Consequently, the H.sub.2 S and COS are customarily either dissociated to elementary sulfur in a Claus furnace or converted to sulfuric acid.
The disadvantages of the conventional art is that on one hand not all gas desulfurization processes are equally well suited for the simultaneous removal of H.sub.2 S and COS, and on the other hand, the processes fulfilling this prerequisite also simultaneously scrub a relatively high portion of carbon dioxide from the stream of gas being scrubbed.
Then a so-called "acid gas" forms with distillation of the changed scrubbing solution. This acid gas has a relatively small hydrogen sulfide and carbon oxysulfide content but has a very large carbon dioxide content. Typically, the composition of such an acid gas is:
______________________________________ 7% by volume of H.sub.2 S 1% by volume of COS 92% by volume of CO.sub.2. ______________________________________
The H.sub.2 S and COS content can be even below these percentages, depending on the particular scrubbing process used. Therefore, the CO.sub.2 scrubbed from the gas flow can be up to 15 times greater than the amount of sulfides.
On account of its low H.sub.2 S content, the carbon dioxide-diluted acid gas is non-combustible and cannot be simply burned with stoichiometric amounts of air to form sulfur dioxide (subsequently reacted to form sulfuric acid) and water vapor in accordance with the equation: EQU H.sub.2 S+11/2O.sub.2 .fwdarw.SO.sub.2 +H.sub.2 O
or to form elemental sulfur and water vapor in accordance with the equation: EQU 3H.sub.2 S+11/2O.sub.2 +3S+3H.sub.2 O.
in order to overcome this disadvantage, it has been proposed that the acid gas liberated from the scrubbing solution be subjected to a further selective scrubbing for the purpose of enriching the H.sub.2 S content. The disadvantage of a second absorption process is that this normally must be performed in several stages; the selectivity of the charged scrubbing medium as a rule is insufficient for attaining the requisite H.sub.2 S concentration in a single step. Therefore, this proposal involves a particularly high apparatus expense as well as high operational costs.
In practice, the conventional art mixes the acid gas with a combustible gas having a high heating value. The resulting mixture is then burned with pure oxygen.
If elementary sulfur is desired, then a certain amount of the elementary sulfur is recycled back through the Claus furnace and is burned together with the mixture of acid gas and combustible gas. The reconducted amounts of sulfur can amount to a multiple of the amount of sulfur contained in the acid gas in the form of H.sub.2 S and COS.
Resorting to the addition of the combustible gas and the pure oxygen means additional expense. This economic disadvantage is accompanied by less output. The recirculation and burning of sulfur in the Claus furnace results in a reduction in the yield of sulfur as well as increased pollution due to a higher sulfur content in the waste gases of the Claus furnace.